Hi Luis,
We have analyzed your query and we are able to reproduce the reported issue. We confirmed that the issue “Misalignment when merging the two header-cell while using stacked headers“ is a defect, and we have logged a defect report. The fix for the issue will be included in our Volume 1, 2018 release which is expected to be rolled out by the month of January, 2017.
Regards,
Manisankar Durai.